從0自學C#13--子類和父類方法的鎖對象問題

調用父類方法時，如何與子類方法，在鎖對象不是同一個執行個體下，能安全執行緒，請見下面三種情況。

case1：

如下代碼，在調用父類的方法時，和子類的方法，發生安全執行緒問題。原因的鎖對象的執行個體不是同一個。

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Threading;namespace ForTest//check the lock object for thread safety{    class Program    {        static void Main(string[] args)        {            son myson = new son();            Parallel.For(0, 5, (int i) =>             {                 myson.methodA();                 myson.methodC();             });            Console.ReadKey();        }    }    public class grandfather    {        //protected static object syncRoot = new object();    }    public class father:grandfather    {        private static object syncRoot = new object();        protected int cont = 0;        public virtual bool methodA()        {            lock (syncRoot)            {                cont++;                Thread.Sleep(1000);                Console.WriteLine("cout++ is " + cont);                return true;            }        }        public virtual bool methodB()        {            lock (syncRoot)            {                return true;            }        }    }    public class son:father    {        private static object syncRoot = new object();        public bool methodC()        {            lock (syncRoot)            {                cont += 2;                Thread.Sleep(2000);                Console.WriteLine("cont += 2 is " + cont);                return true;            }        }    }}

輸出：

cout++ is 1cout++ is 4cont += 2 is 5cout++ is 5cout++ is 8cont += 2 is 9cout++ is 11cont += 2 is 11cont += 2 is 13cont += 2 is 15

case2：

case1的解決方案是，在父類初始化鎖對象，讓子類繼承。這樣就安全執行緒了。如下。

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Threading;namespace ForTest//check the lock object for thread safety{    class Program    {        static void Main(string[] args)        {            son myson = new son();            Parallel.For(0, 5, (int i) =>             {                 myson.methodA();                 myson.methodC();             });            Console.ReadKey();        }    }    public class grandfather    {        protected static object syncRoot = new object();    }    public class father:grandfather    {        protected int cont = 0;        public virtual bool methodA()        {            lock (syncRoot)            {                cont++;                Thread.Sleep(1000);                Console.WriteLine("cout++ is " + cont);                return true;            }        }        public virtual bool methodB()        {            lock (syncRoot)            {                return true;            }        }    }    public class son:father    {        public bool methodC()        {            lock (syncRoot)            {                cont += 2;                Thread.Sleep(2000);                Console.WriteLine("cont += 2 is " + cont);                return true;            }        }    }}

輸出：

cout++ is 1cout++ is 2cont += 2 is 4cout++ is 5cout++ is 6cout++ is 7cont += 2 is 9cont += 2 is 11cont += 2 is 13cont += 2 is 15

case3：

當然有些特殊情況下，子類硬要重新執行個體化一個鎖對象。如何避免上面第一種安全執行緒問題發生？需要：

子類加鎖重寫父類分方法（如果父類methodA是虛方法）

或者

new一下（如果父類methodA是執行個體方法）。

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Threading;namespace ForTest//check the lock object for thread safety{    class Program    {        static void Main(string[] args)        {            son myson = new son();            Parallel.For(0, 5, (int i) =>             {                 myson.methodA();                 myson.methodC();             });            Console.ReadKey();        }    }    public class grandfather    {        protected static object syncRoot = new object();    }    public class father:grandfather    {        protected int cont = 0;        public virtual bool methodA()        {            lock (syncRoot)            {                cont++;                Thread.Sleep(1000);                Console.WriteLine("cout++ is " + cont);                return true;            }        }        public virtual bool methodB()        {            lock (syncRoot)            {                return true;            }        }    }    public class son:father    {        private static object sync = new object();        public override bool methodA()//重寫        {            lock (sync)            {                return base.methodA();            }        }        public bool methodC()        {            lock (sync)            {                cont += 2;                Thread.Sleep(2000);                Console.WriteLine("cont += 2 is " + cont);                return true;            }        }    }}

或

 public new bool methodA()\\new一下        {            lock (sync)            {                return base.methodA();            }        }

輸出：

cout++ is 1cout++ is 2cont += 2 is 4cout++ is 5cout++ is 6cout++ is 7cont += 2 is 9cont += 2 is 11cont += 2 is 13cont += 2 is 15

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